This application claims the priority of German Application No. 197 02 311.8, filed on Jan. 23, 1997, and U.S. Provisional Application Ser. No. 60/037,950, filed Feb. 20, 1997, the disclosures of both of which are expressly incorporated by reference herein.
The invention relates to a growth substrate having growth nuclei made of diamond and/or diamond-like carbon arranged on its growth surface as well as to a process for a uniform nucleation on the growth substrate. This invention is based on the article "Nucleation of High Oriented Diamond on Silicon via an Alternating Current Substrate Bias" by Wolter, et al. in Appl. Phys. Lett., Vol. 68, No. 25, Jun. 17, 1996, Page 3558-3560.
From the Wolter Article it is known to apply an alternating BIAS voltage of a plasma CVD process for nucleation on a growth substrate made of silicon and arranged in an evacuated reactor and pretreated, by growth nuclei made of diamond and/or a diamond-like carbon. As a result, a higher nucleus density of high-precision oriented growth nuclei in comparison to direct-current-type bias voltage is achieved on the growth substrate in otherwise similar conditions. High-precision orientation relates to growth nuclei whose orientation deviates by less than 10.degree. from the crystal orientation defined by the growth substrate corresponding to Miller's indices (h, k, l). Despite the high nucleus density, the nucleation is highly inhomogeneous; that is, high lateral fluctuations occur in the density of high-precision oriented growth nuclei over the whole growth surface of the growth substrate.
From PCT patent application WO 94/08076, it is known for the nucleation on a Si growth substrate to pretreat the Si growth substrate and then provide the nucleation on it in a plasma CVD process from a gaseous phase. For the pretreatment, the growth substrate is installed in a reactor; the reactor is preferably evacuated to less than 10.sup.-9 mbar; and the growth substrate is heated to more than 950.degree. C. As an alternative or supplementation, the growth surface can also be subjected to a plasma treatment which preferably takes place by means of an almost 100% hydrogen plasma at substrate temperatures of between 300.degree. C. and 1,100.degree. C. In this case, it is advantageous to apply a bias voltage of between +50 and -300 v, particularly of approximately -50 v, to the growth substrate. After the cleaning, the nucleation can start in a known manner, the bias voltage advantageously being maintained. For example, CO and CH.sub.4, C.sub.2 H.sub.5 OH, acetylene and acetone or, for example, CF.sub.4 and methane can be used as the process gases. A preferred combination is hydrogen and methane.
The nucleus density which can be achieved by means of this process is high but the nucleation is highly inhomogeneous because few to almost no high-precision oriented growth nuclei are formed in the center of the growth substrate.
It is an object of the invention to produce a growth substrate with a nucleus density which is more homogeneous over the surface than previously.
According to the invention, this object is achieved by a growth substrate having growth nuclei made of diamond and/or diamond like substances arranged on its surface with over 50% of the nuclei deviating less than 10.degree. from the crystal orientation defined by the substrate according to Miller's indices. A manufacturing process is also defined.
Additional suitable embodiments include a nucleus density between the center of the growth substrate and a distance of maximally 15 mm from the center changing by maximally 50, 30 and 20%, a nucleus density in the center of the growth substrate of 1.10.sup.8 nuclei per cm.sup.2 and 3.times.10.sup.8 nuclei per cm.sup.2, and a nucleus density between the center of the growth substrate and a distance maximally 15 mm from amounts to between 1.times.10.sup.8 nuclei per cm.sup.2 and 5.times.10.sup.8 nuclei per cm.sup.2 and 3.5.times.10.sup.8 nucleii per cm.sup.2 and 5.10.sup.8 nuclei cm.sup.2.
Suitable embodiments of the process claims include employing bias voltages between -30 and -130 volts, frequencies between 1 and 100 Hz, 1 and 10 Hz, and a frequency at 5 Hz. Process embodiments also include varying active (t.sub.on) and currentless (t.sub.off) voltage values and using growth substrates of silicon and .beta.-silicon carbide.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.